This invention relates to modifying the behavior of fish. Specifically, it modifies fish behavior by using oscillating water particle acceleration, visual cues, and water currents.
Systems have been designed and installed to deter or guide fish from certain underwater areas. These areas include water intakes for hydroelectric power plants, municipal water intakes, thermal power plants, and irrigation systems. Fish can suffer high mortalities when they come in contact with pumps or turbines, when they are subject to temperature variations induced by plants, or when they are pumped through irrigation systems and discharged onto fields.
These systems used to deter or repel fish can be broken down into two categories: physical barriers and behavioral deterrents. These devices and their advantages and disadvantages are described in Taft, E.P. 1986. Assessment of Downstream Migrant Fish Protection Technologies for Hydroelectric Application. Stone and Webster Engineering Corporation. Electric Power Research Institute, Palo Alto, Calif. Physical barriers work by limiting the opening size of the plant intake such that a certain fish species or life stage of fish cannot enter. This includes barriers such as closely spaced bar racks, traveling screens, and fixed screens. The disadvantages of these structures are that they are difficult and expensive to construct and maintain. They can also limit the flow of water into the intake, thereby limiting power production or quantity of water available. These structures can also result in impingement of fish on the intake.
This patent is in the behavioral deterrent category. Behavioral deterrents generate certain stimuli of which fish are known to respond, and utilize these stimuli to deter or repel fish from certain areas. Known systems have employed such devices as underwater lights, electric fields, water current/turbulence generators, visual leads such as traveling cables, and sound generators. Underwater lights (including strobes) are species-specific, and the visibility of lights, and therefore their effectiveness, is reduced in turbid water. Major concerns with underwater electric fields include a concern for human safety, the variability of the field strength depends on the conductivity of water and the length of the fish, and the fact that the field strength that is effective for some fish species may be lethal to other species.
Recently, mechanically generated water currents have been used as both a deterrent to fish and to mimic the natural water current in the river. The use of mechanically generated water currents and turbulence to guide fish is summarized in Coutant, C.C. 1998. Turbulent Attraction Flows For Juvenile Salmonid Passage at Dams. Oak Ridge National Laboratory, Oak Ridge, Tenn. The use of water current and turbulence generators as a deterrent, such as air bubble curtains and water jets, is usually energy intensive and doesn""t affect some species. Mechanically generated currents used to mimic natural river currents guide fish by creating a predominant surface current (for surface-oriented fish) across the plant intake to the area of a fish bypass. Therefore, this current has to compete with the variable river currents. It is sometimes difficult to establish this continuous lead over long distances with multiple current generators without creating gaps in the current.
Visual cues can be an effective behavioral deterrent. J. R. Brett, and D. F. Alderdice documented the use of traveling hanging cables to direct fish movement in Research on Guiding Young Salmon at Two British Columbia Field Stations. Fisheries Research Board of Canada, Ottawa, 1958. Although this showed promise, there are operational problems with the system because debris in the river is likely to get tangled in the cables. Water clarity is also important with this system.
Sound is an additional means of modifying the behavior of fish. An overview of the current state of the art sound deterrent systems is provided in Carlson, T. J. 1994. Use of Sound for Fish Protection at Power Production Facilities: A Historical Perspective of the State of the Art. Battelle, Pacific Northwest Laboratories. U.S. DOE Bonneville Power Administration, Portland, Oreg.
There are several disadvantages to recent sound deterrent systems. One of the disadvantages of underwater sound deterrents is that it is difficult to establish an uninterrupted barrier, and thus create a continuous lead for fish to follow away from the power plant intake area. Also, the frequency and amplitude of the sound wave must be tuned for each individual species, and even life stage, of fish. Underwater sound systems may be categorized into either high frequency systems or low frequency water particle motion or infrasound systems, depending on the specific species of fish to control. Low frequency sound systems have been proven to elicit an avoidance response in Atlantic salmon smolts, Atlantic cod, and perch in Knudsen, F. R., P. S. Enger, and O. Sand. 1992 Awareness Reactions and Avoidance Responses To Sound in Juvenile Atlantic Salmon Smolt, Salmo salar L. Journal of Fish Biology. 40: 523-534. To be effective, a sound deterrent must be able to create the same sound repeatedly for extended periods of time without breakdown. The problems the Sand system developed were that it was not mechanically reliable and that it involved the risk of electric shock. Other sound deterrents developed since then are more reliable but have difficulty creating a continuous barrier to the fish because the sound generators are at point sources, such as U.S. Pat. No. 5,730,086 issued to Truebe. Also, it has been shown in certain instances that a strong background noise (white noise), such as that due to turbine operation, can blanket over the effect of the sound deterrent. Without any additional deterrent, the fish are free to enter possibly hazardous areas.
Accordingly, several objects and advantages of my invention are:
To provide a cost effective fish deterrent and guide.
To provide a fish deterrent and guide that incorporates multiple behavioral deterrents to increase effectives.
To provide a fish deterrent and guide that is adjustable for different site conditions.
To provide a fish deterrent and guide that will facilitate routine plant operations by bypassing trash around the plant intake.
To provide a fish deterrent and guide which keeps fish in their river environment to reduce disease transmission and boost public relations.
To provide a fish deterrent and guide which improves the river conditions for migrating fish.
To provide a continuous fish deterrent and guide.
To provide a fish deterrent and guide that will assist upstream migrating fish in finding a fishway entrance.
To provide a fish deterrent and guide that increases fish bypass effectiveness by reducing the velocity gradient in the fish bypass entrance area.
Further objects and advantages of the invention will become apparent from a consideration of the drawings and ensuing description.